Control of film advance in a camera can be done in a variety of ways. For example, there are known cameras having microprocessors with sufficient logic to provide a controlled and motorized frame by frame metering of the filmstrip. Sensing of frame registering perforations of the filmstrip in such systems can be done, such as by using optical sensors or other switching controls. These techniques and the use of motorized film advance mechanisms are quite expensive and significantly impact the cost of the camera into which they are incorporated.
Manually operated film advance systems are also known. For example, U.S. Pat. No. 4,437,751 describes a film transport mechanism in which a double sensor engages the end-of-film perforations of a filmstrip. The engagement of the sensor with the perforations causes a separate locking lever to be activated, prohibiting further advancement of the filmstrip. In addition, a separate button on the camera must first be depressed in order to retract the double sensor, for allowing subsequent rewind of the filmstrip into the film cartridge.
Though the above described double sensor provides a technique for detecting the end of the usable portion of the filmstrip, a separate mechanism is still required in order to stop the further advance of the filmstrip. In addition, it is necessary to cause retraction of the sensor in order to effectively rewind the filmstrip.
As evidenced by typical manual film advance systems, such as the one described above, discrete subsystems are necessary to coordinate the shutter release, the film advance and metering, and the film rewind mechanisms in the camera. These subsystems involve the use of many mechanical components which increase the size of the camera, or alternatively provide for combinations of mechanical and electrical driven components which significantly impact the cost of the camera.
There is a need to provide a manually operable metering mechanism for a photographic camera which is simple in design so as to effectively prevent further advancement of a filmstrip when metering, while allowing the filmstrip to be rewound without independent mechanisms being required for retraction of the metering mechanism.
There is a further need to provide a simple and reliable mechanical mechanism for a photographic camera which provides for automatic cooperation between film advance, shutter release and film rewind with a minimum number of components.